Crystal Chemistry of Natural Tellurides. I: Refinement of the Crystal Structure of Sylvanite, AuAgTe4

Electron microprobe analyses and the refinement of the crystal structure indicate, that sylvanite, AuAgTe4, from Baia de Aries (=Offenbanya), Romania, has a stoichiometric composition and an ordered crystal structure (a-8.95(1) A, b=4.478(5) A, c=14.62(2) A; β=145.35(5)supo; Z-2; space group P2/c-Csub(2h)4). The Au atom is surrounded by six Te atoms in a [4+2] coordination as characteristic for oxidation state III. Around the Ag atom (oxidation state I) are also six Te atoms, but arranged in a [2+2+2] coordination. Via common edges the AuTe6 and AgTe6 polyhedra build up 'sheets' parallel to (100). These 'sheets' are combined to a network of Te2 dumbbells (Te-Te=2.82 A). (Author)